The DC-6 was known as the C-118 Liftmaster in
United States Air Force
service, and as the R6D in United States
Navy service prior to 1962, after which all U.S. Navy variants
were also designated as the C-118.

Design
and development

The United States Army Air
Forces commissioned the DC-6 project as the
XC-112 in 1944. The Air Force wanted an expanded,
pressurized version of the popular
C-54 Skymaster
transport with improved engines. By the time the XC-112 flew, the
war was over, and the USAAF had rescinded its requirement.

Douglas converted its prototype into a civil transport
(redesignated YC-112A, having significant differences from
subsequent production DC-6 aircraft) and delivered the first
production DC-6 in March 1947. However, a series of mysterious
in-flight fires (including the fatal crash of United Airlines Flight 608)
grounded the DC-6 fleet later that year. The cause was found to be
a fuel vent located adjacent to the cabin cooling turbine intake.
All DC-6s in service were modified to correct the problem, and the
fleet was flying again after just four months on the ground.

Operational
history

Passengers deplaning an SAS DC-6. Note the upper row of windows,
indicating this was built as the optional sleeper variant of the
original length DC-6

Pan Am
used DC-6B aircraft to inaugurate its first trans-Atlantic tourist
class flights, starting in 1952.

Douglas designed four basic variants of the DC-6: the "basic
DC-6," and the longer fuselage, higher-gross-weight, longer range
versions—the "DC-6A" with large cargo doors forward and aft of the
wing on the port (left hand side) with a cargo floor, the "DC-6B"
designed for passenger work, had passengers doors only and a
lighter floor and the "DC-6C" a "convertible" aircraft built with
the 2 cargo doors, but fitted with removable passenger seats. The
DC-6B, originally powered by Pratt & Whitney
R-2800-CB-16 engines with Hamilton Standard 43E60 constant
speed reversing propellers, was regarded as the ultimate
piston-engine airliner from the standpoint of ruggedness,
reliability, economical operation and handling qualities. The
military version, essentially similar to the DC-6A, was the USAF
C-118 Liftmaster, and the USN R6D which used the more powerful
R-2800-CB-17 engines. The more powerful engine was later used on
the commercial DC-6B to accommodate international flights. The Navy
version (in the late 1950s and early 1960s) had Curtiss Electric
constant-speed reversing propellers.

The USAF and USN renewed their interest in the DC-6 during the
Korean War, and
ordered a total of 167 C-118/R6D aircraft, some of which later
found their way into civilian service. Harry Truman's first
presidential aircraft was an Air Force VC-118
called "The Independence".

Total production of the DC-6 Series was 702 including military
versions.

In the 1960s, two DC-6s were used as transmitter platforms for
educational television, based at Purdue University, in a program
called MPATI (Midwest Program for Airborne Television
Instruction).[1]

Many older DC-6 aircraft were replaced in airline passenger
service by the Douglas
DC-7, but the simpler, more economic engines in the DC-6 has
meant that this type has out-lived the more sophisticated DC-7.
DC-6/7s surviving into the Jet Age were replaced in front line
service by Boeing 707
and Douglas DC-8
aircraft.

2006 marked the 60th anniversary since the introduction of the
DC-6.

Variants

UAL DC-6 at Stapleton Airport, Denver, in September 1966

Pan Am DC-6B at London Heathrow in September 1954 on a tourist
flight

XC-112

United States military designation of an improved version of
the C-54 (DC-4); became the prototype DC-6. Eventually designated
YC-112A, pressurized, P&W R-2800-83AM3
engines

On February 14, 1953, National Airlines Flight 470 crashed into
the Gulf of Mexico off Mobile, Alabama. The aircraft broke up
in the turbulence of a "frontal wave" storm after failure of the
left wing; all 41 passengers and five crew members were
killed.